Quagga Posted March 23, 2017 Posted March 23, 2017 I am asking for XC riding, I know that enduro and downhill have other extremes. What is the general opinion on asymmetric rims vs the normal ones. "They" say it improves the spoke tension and angle, but my other question then is how does a deeper rim profile affect the spoke angle etc. I see there is a trend for deeper rims, more around 28-32 mm (especially carbon ones) in both profiles. Deeper rim = shorter spokes, but more angle Asymmetric should fix angle, but how deep does one go? Also, how much wider than normal is good. AC makes 30mm ID but there are some 31-33 ID rims out there. At what point do you think it becomes too wide. How does one know at what point your frame will not handle a wider rim any longer? Specialized Epic comes out with 21mm but you can run AC 30mm as far as I know. But can you fit 32mm with 2.3 Tyres? What is the general feeling? Opinions?
JanJan Posted March 23, 2017 Posted March 23, 2017 I think the progression of assymetrical rims halted completely when the Boost hubs development started, as SRAM and Shimano didn't have to reduce the hub's length further. Assymetric wheels do have ther advantages, but for the different spoke hole patterns on the rims which adds machining time and costs, I do not foresee the fancy technology to trickle down to normal XC riding. Regarding the rim/tyre width: Rims wider than 30 mm and rear tyres wider than 2.1 would be considered 'heavy' for XC applications.
nick_the_wheelbuilder Posted March 23, 2017 Posted March 23, 2017 Don't stress about the fads. Get rims 24-30mm wide internally, don't worry about asymmetric ones - no massive pros or cons for XC, as long as the wheels are built properly with quality spokes and nipples by a builder who knows his stuff you'll be fine. Asymmetrical rims may result in a wheel a few % stiffer..... you probably wont notice it.
Captain Fastbastard Mayhem Posted March 23, 2017 Posted March 23, 2017 I am asking for XC riding, I know that enduro and downhill have other extremes. What is the general opinion on asymmetric rims vs the normal ones. "They" say it improves the spoke tension and angle, but my other question then is how does a deeper rim profile affect the spoke angle etc. I see there is a trend for deeper rims, more around 28-32 mm (especially carbon ones) in both profiles. Deeper rim = shorter spokes, but more angle Asymmetric should fix angle, but how deep does one go? Also, how much wider than normal is good. AC makes 30mm ID but there are some 31-33 ID rims out there. At what point do you think it becomes too wide. How does one know at what point your frame will not handle a wider rim any longer? Specialized Epic comes out with 21mm but you can run AC 30mm as far as I know. But can you fit 32mm with 2.3 Tyres? What is the general feeling? Opinions?Okay. Firstly - rim width does not significantly affect tyre width. All it does is "square" off the tread. Overall tyre width remains largely the same across rim sizes - all that changes is the distance between the beads. See below: Tire tread measured on a 40mm wide rim (34mm internal), edge knobs stand up and flair slightly less to the sides Same size tire tread measured on a 28mm narrow rim (24mm internal) As for assymetric vs normal - assymetric rims will allow you to build a stiffer theoretically wheelset, as the spokes will be of equal length and therefore the structure will be more of an isosceles triangle as opposed to a normal rim's right angled triangle. Simple mechanics, really. If both side spokes have the same angle, then the structure will be stiffer than if one side were longer than the other (all things remaining equal, of course). But I'm not sure on the actual % values. I just like the idea of equal spoke lengths. Makes replacement far easier IMO Deeper rim profile will have the same effect, as the spokes get shorter and the ratio of height:width reduces (a squat triangle is more stable than a tall triangle) ITO tyres fitting to a wide rim, yes you can fit a 2.3 to a 32mm internal rim. I'm running 2.35's on a 35mm internal width rim, and they're performing brilliantly. Some tyres will perform better on wider rims, due to the side knob orientation. Generally speaking, the rounder the profile, the better it will adapt to wider rims. If the side knobs are too "straight" they may square off too much and result in excess wear when you lean it over (which is why Maxxis are making their Wide Trail tyres now - they're built with wide rims in mind and a slightly rounder profile than the normal ones) I've heard of great success even with 2.1" tyres on 35mm wide rims (ask Neville of Bike Mob about hit experiences, and Iwan re his experiences with skinny Racing Ralphs on wide rims) and the wide rims really do lend additional support to the tyre, allowing lower pressures, increased grip and lower rolling resistance. Insofar as how wide is too wide - I'd say personal preference, weight preference and tire profile come into play. Happy medium tends to be 28-32mm depending on who you speak to. Would I swap out my wide rims for narrower ones? Never.
Quagga Posted March 23, 2017 Author Posted March 23, 2017 Thanks for all the replies... So it si safe to say that I should be able to fit any rim from a 21mm to 32mm internal on my specialised Epic for excample. Just the bead will be furthur appart?
Captain Fastbastard Mayhem Posted March 23, 2017 Posted March 23, 2017 Thanks for all the replies... So it si safe to say that I should be able to fit any rim from a 21mm to 32mm internal on my specialised Epic for excample. Just the bead will be furthur appart?Correct.
David Marshall Posted March 23, 2017 Posted March 23, 2017 If memory serves me right DT claimed a jump from 56:100 to 70:100 for an offset spoke bed rim which is quite significant. Spoke lengths will still be determined by the hub design rather than the rim offset as you would not be able to move the centre line enough to balance the spokes perfectly. A deeper rim section generally strengthens the rim, in my opinion more than the -ve effect of the shorter spoke. When 29" MTB's first came out we used to build wheels with Velocity Fusion or Mavic CXP33 road rims for the heavy weights. Not pretty (brake surface) but very strong!
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